1. Field of the Invention
The present invention relates to a copying apparatus provided with an automatic document feeder capable of serially placing a pair of original documents at a specified position on a platen, and discharging them from the platen after the completion of exposure.
2. Description of the Prior Art
To reduce a time for replacing original documents or to eliminate type procedure for the document replacement, various copying apparatuses provided with an automatic document feeder (hereinafter abbreviated as ADF) have been recently developed and commercially available. Such an ADF constitutes means for reducing indirect costs (time and labor). In contrast, to reduce direct costs (supplies, such as copy sheets and toner), several methods available are as follows: a duplex copying method, wherein two documents are copied to both sides of one copy sheet; and a method for reducing and copying two documents to one side of a copy sheet having the same size as each original document (two-document, single-face copying mode). In the former method, a pair of documents are unchangedly copied to one side of a copy sheet, while toner making for two copies is consumed. In contrast, the latter method is economical in that a copy sheet and toner each for only one sheet of document is consumed per two duplicates. Furthermore, when the above two methods combined, the result is extreme economization, since four documents are copied using both sides of one copy sheet.
Various conventional ADFs, however, feed documents one by one onto a platen. Accordingly, to perform two-document, one side copying, an operator is supposed to replace documents and place them on the platen per sheet of document, thus time and labor are not reduced.
To solve such disadvantages, improvements have been disclosed in the following patents, although all of them incur some problems. For example, an ADF for feeding two documents serially onto a platen in the direction of the document feeding has been disclosed in Japanese patent Laid Open Publication Nos. 60-2942, 60-84945 and 60-93452. This type of ADF, however, has the following disadvantages originated from the relationship between the document size and the copy sheet size, when the dual document feeding mode has been selected. More especially, using the dual feeding mode, the proper magnification of a duplicate cannot be determined for the serially placed two documents, regardless of the size of the two documents transported on the platen, when the sizes of the copy sheets fed from the sheet feeder in the copying machine are of latitudinal positioned A4 or B5 size i.e. the shorter side thereof has been set in the sheet feeding direction. If the copying operation is performed under such a condition, the obtained duplicate will be incomplete with a part of image missing.
Furthermore, the dual document feeding cannot be performed, if an odd number of documents are processed, even through the dual feeding mode has been selected. This is because documents are fed in pairs, and only the final document remains without being formed into a pair. Therefore, to solve such a disadvantage, the ADF disclosed in said Japanese Patent Laid Open Publication No. 60-93462 has the following feature: When performing duplex copying according to the book divisional copying wherein image exposure scanning is executed on one side of opened book, the ADF is controlled in such dual feeding mode. When the final independent document that has been fed in the dual feeding mode is copied, the copy sheet having on its one side a copy image is discharged outside the copying machine. This method, however, has the following disadvantages: Since the dual feeding mode is controlled based only on the combination of book divisional copying and duplex copying, a problem is present in regard to more flexible operation.